Various roofing structures and systems are known. The object of most roofing systems is to provide insulation for the building which the roof covers, to keep the building dry, and yet to prevent water vapor from accumulating within the roofing system or structure. Accumulation of water vapor is damaging or destructive to the roofing system. Yet it is difficult to keep water out of the building and at the same time to prevent build-up of water vapor within the roofing structure. In addition, the roofing system must be strong enough to support any wind loads and snow loads to which it is subjected, to permit a person to walk on the roof, and (where desired) support an esthetically pleasing exterior member which constitutes the top layer of the roofing structure. Existing roofing systems achieve the aforesaid objects with varying degrees of success. In some cases there is a trade-off in which performance in one area is sacrificed in order to achieve top performance in another area. In particular, it is difficult to keep a building dry and at the same time to prevent the buildup of water vapor within the roofing structure. Various constructions have been proposed in order to achieve both objects.
U.S. Pat. No. 4,021,981 to Van Wagoner discloses a roofing system which comprises an insulation course and a protective layer, the former being placed atop a vapor impermeable membrane. The insulation course may be made of an expanded foam, e.g. polyurethane or polystyrene, glass beads, insulating concrete or bituminous blocks. The protective course is a fire-retardant material which is water but not vapor impermeable. Various materials are suggested, and a fiberglass reinforced surface bonding cement containing an acrylic polymer emulsion additive is disclosed is preferred.
U.S. Pat. No. 3,619,961 discloses, as a roof deck material, a foamed polystyrene board having channels therein to permit the escape of water vapor. Polystyrene board may be situated on a suitable base member such as concrete, and on top of this board may be placed an additional insulating layer, (e.g. light weight insulating concrete) and a water impermeable (e.g. bituminous coated roofing felt) top layer.
U.S. Pats. Nos. 3,135,069 to Schuller et al. and 4,189,886 to Frohlich et al. show other roofing structures with various layers through which air and water vapor may pass.
U.S. Pat. No. 3,598,688 to Bellamy shows a roofing construction which includes a waterproof layer and a wear resistant layer having vent openings therethrough at periodic intervals.
While various roofing constructions have been proposed, none has fully achieved the various desired characteristics of a roofing system, such as those noted above.